Chair backrest



FIG. 1 is a perspective view of chair backrest showing my new design;

FIG. 2 is a front view thereof;

FIG. 3 is a rear view thereof;

FIG. 4 is a left end view thereof;

FIG. 5 is a right end view thereof;

FIG. 6 is a top view thereof;

FIG. 7 is a bottom view thereof;

FIG. 8 is another perspective view thereof; and,

FIG. 9 is a perspective view of the chair backrest showing my new design connected to a support unit, wherein the broken lines in the drawing is for illustrative purpose only and shows the portion that forms no part of the design to be claimed. 

CLAIM The ornamental design for a chair backrest, as shown and described. 